Develop Reference

Figuring out where to store local files in Java

For reasons that I guess are outside the scope of this question, I want to move a program that I have written for use with Java Web Start to stop using JWS and distribute it as an ordinary Jar file instead.
My main problem with this plan is how to figure out where to store files in a nice manner in Java, assuming I'm going to run on different platforms (though I depend on JOGL as well, so there's no great risk of running on horribly esoteric platforms, at least). My program stores various pieces of local data, mostly for caching or "caching-like" purposes -- it's extremely nice to be able to keep it, but it's not a complete disaster if the data is lost.
I currently use the JNLP PersistenceService for this purpose, so moving out of JWS I'll need to figure out some directory to store files in instead. Consider this:
File datadir = new File(System.getProperty("user.home"), ".myprogram");
I figure this works well on Unix and Unix-like platforms, but it's clearly ugly, at least, on some platforms like Windows where I guess I should use the AppData directory or whatever it's called again.
My current line of thought is to use this datadir as a default fall-back everywhere except on known platforms where I replace it with something better, like Windows. The questions I have about this are these:
Is this a reasonable default to begin with? I'm kind-of-fine with this failing on some unknown platforms; I'll just silently disable caching and some extended features if this is the case, but could it fail in some manner that leaves actively bad results?
Is there any good way to figure out I'm on Windows? The best thing I can figure out right now is to match some patterns against os.name, which I guess should work well enough, but is there a better way? I don't intrinsically mind testing with reflection to see if some sun.* packages exist that could help out or something (with the risk of falling back to defaults), if that is good. (Question applies in general to all platforms; are there any somewhat robust idioms for figuring this out in general?)
Is there a good way to figure out the directory to use on Windows? Using static paths seems ugly since I know they can be overridden with registry settings, or be localized and whatnot.
Are there any other platforms I should think of from the outset? My datadir should work fine on OSX, right?
Is there any better alternative altogether?

Consider using the java.util.prefs.Preferences API for this purpose.

If it's just cached data that is replaceable I would just recommend using the temp directory.
See:
new File(File.createTempFile().getParent(), 'my-file-name');
You can set it to be destroyed on your app shut down or just leave it there.
If you want more of a semi-permanent but out of the way storage you may need to care what OS you're on and act accordingly like the answers to this question

How can I distribute my java applications for user ease?

I'm really confused - but really it's pretty wierd because I know two programming langauges but I can't figure out something simple like this...
I've been looking for ages but I can't seem to get my head around it.
You See, for a long time I've been writting in AutoIt, and I've written two programs in it that are due to go on sale soon! They were never meant to be out for a long time though (kind of like Windows Vista), so lately I've been learning Java with success. I've wrote a few very very simple applications in eclipse while going through Java tutorials! I'm now ready to transfer my programs to Java, to gain me a wider market due to Java's cross-platform ability, but I never anticipated distribution to be this complex.
My first problem I have come across is ease of use on multiple OS's: I don't want my customers to have to deal with JRE or multiple files, I need a double click solution that will work on MAC, Windows, Linux, etc so that even complete computer newbie's can launch my software! Secondly, this is not as much a problem as something I am not sure how to do. This is including files in my software package some need to stay seperate from the program but others could be compiled, but actually I suppose this can be worked around by an installer - which would probably be easier! And finally the other proram I made is stand - alone so it can work on USB sticks (which what it was designed for), now, how do you suppose I do this so it will launch on multiple opearating systems when it's plugged in without any hasle?
Update :: Forgot to add :: My concerns about security
I have read and from personal experience I know: how easy it is to decompile a .jar, and if there not protected properly read the source code! I know about obfuscation and I know I'll have legal back up but it just worries me. Even from the point of view that user may get the wrong first impretion of my software.
So to conclude in one sentace (Please read above still):
I need to be able to let people use my software written in Java by double clicking e.g. Like something made in AutoIt - a standard application i.e *.exe
Thanks in advance

There are two routes you can take without needing any extra software involved.
The first is to just make an executable jar (Java Archive) file. Java automatically associates the .jar extension with the Java interpreter on most systems. The JAR's manifest file will tell it which class to launch when you double-click it.
The second, less recommended route, is to make a Java Web Start application, with a JNLP launcher file. The is aimed more at applications distributed from web sites.

I'll suggest the third way: write several platform-specific launch scripts for your application. For example, run.bat for Windows and run.sh for Linux. Inside every script write a command to run JRE with all the necessary parameters. You can also maintain some pre-launch checks (is JRE installed?) or some platform-specific actions in this scripts.

Combining Java and C without gcj -- move C to Java or Java to C?

First, I have no experience doing this. But like the beginning of any good program, I have problem that I need to fix, so I'm willing to learn.
So many of you are probably already familiar with pdftk, the handy utility for handling various pdf-related tasks. So far as I can tell, most of these features are available in much newer, lighter libraries/extensions, except the one I need (and probably the only reason it still exists): merging form data files (fdf and xfdf) with a form PDF and getting a new file as the output.
The problem is that my server doesn't have gcj, which is fundamental to build/compile pdftk. I don't know if it's because I'm on Solaris or if it's for some other sysadmin-level reason, but I'm not getting gcj anytime soon. And there are no pre-compiled binaries for Solaris as far as I can find.
So I'm thinking that the MAKE file and C code can be rewritten to import the Java library (very ancient version of itext) directly, via javac.
But I'm not sure where to really start. All I know is:
I want a binary when I'm done, so that there won't be a need for a Java VM on every use.
The current app uses GCJ.
So my first thought was "Oh this is easy, I can probably just call the classes with some other C-based method", but instead of finding a simple method for doing this, I'm finding tons of lengthy posts on the various angles that this can be approached, etc.
Then I found a page on Sun's site on how to call other languages (like C) in a Java class. But the problems with that approach are:
I'd have to write a wrapper for the wrapper
I'd probably be better off skipping that part and writing the whole thing in Java
I ain't ready for that just yet if I can just import the classes with what is already there
I'm not clear on if I can compile and get a binary at the end or if I'm trapped in Java being needed every time.
Again, I apologize for my ignorance. I just need some advice and examples of how one would replace GCJ dependent C code with something that works directly with Java.
And of course if I'm asking one of those "if we could do that, we'd be rich already" type questions, let me know.

I'm not sure what you are looking for exactly, so I provided several answers.
If you have java code that needs to run, you must:
Run it in a jvm. You can start that vm within your own custom c-code, but it is still using a jvm
Rewrite it in another language.
Compile with an ahead-of-time compiler (eg gcj)
Incidentally, you could compile a copy of gcj in your home folder and use that. I believe the magic switch is --enable-languages=java,c (see: here for more)
If you have c-code you want to call from java, you have four options:
Java Native Interface (JNI). It seems you found this
Java Native Access (JNA). This is slower than JNI, but requires less coding and no wrapper c-code. It does require a jar and a library
Create a CLI utility and use Runtime.Exec(...) to call it.
Use some sort of Inter Process Communication to have the Java code ask the c-code to perform the operation and return the result.
Additional platform dependent options
Use JACOB (win32 only: com access)

I am not sure if I understand what you are looking for.
If you are looking to incorporate the C code into Java to make a native binary without the gcj, I think you are out of luck. You can include the C in Java, but it would be a primarily Java program meaning you would need the JVM on each run. Is there anything stopping you from compiling the gcj yourself?

Baffling Failure to Call External Executable From Within Java Program

All right, I've hit a bug that has simply confused the bejeebus out of me. I'm looking for ideas about what it could be that I can investigate, because right now, I got nothing. It goes something like this:
I have a standalone Java application that occasionally needs to twiddle the Line-In volume of the computer it's running on (a WinXP machine). It does this by calling a pair of external executables (written in VB6*) that can get and set various component volumes. (They can handle Line-In, Mic, Wave, CD, and the master volume control.)
There are several hundred units in the field, running on hardware (Dell machines) that my company provided and controls. At least several dozen clients are using this feature, and it works perfectly -- except for one instance.
For this one troublemaking machine, it simply doesn't work. I watch the volume sliders when the app is running, and when the volume is supposed to drop, they stay put. When I check the app's log file, it throws no errors, and appears to be executing the code that drops the volume. When I run the executables from the command line, they work perfectly.
I can't vouch for this machine being 100% identical to all the ones that are behaving properly, but we've been buying the same line of Dells for quite some time now; at a bare minimum, it's very, very similar.
So, turning my confusion into a bullet list:
If I'm doing something stupid in the Java code (i.e., not clearing my STDOUT/STDERR buffers), why is it only an issue on this machine?
If there's something broken in the VB6 executables, why do they work on every other machine and on this machine from the command line?
If there's some sort of hardware oddity on this machine, what sort of oddity could cause the volume control executables to fail only when called from within a Java application?
I am very confused. I do not like being confused. Anybody have any suggestions that may lead to my enlightenment?**
-* -- I know, I know, VB6, 1998 called and they want their obsolescent proprietary bug generator back, etc. Wasn't my decision. But the code works. Usually.
-** -- Insert Buddhism joke here.
Update Edit: Customer service may have stumbled onto something; it may be something to do with client configuration settings in the database. New evidence suggests that either something's misconfigured for that client or my software is doing something stupid in response to a specific configuration. And the problem may be more widespread than we thought, due to this particular feature not being as commonly used as I thought.
Responding to the comments:
Debugger: Theoretically possible, but looks like a massive headache given our setup.
High Verbosity Logging, Java: Good idea this, particularly given than the problem may be more widespread than I originally believed. Time to start revisiting some assumptions. And possibly clubbing them. Like baby seals.
High Verbosity Logging, VB6: A possibility; will need to be rolled-into the high-verbosity Java logging to trap the output, since my VB6-fu is so pitiably weak I don't know how to output text to a file. But, yeah, knowing whether or not the script is even getting called would be valuable.
Window Event Viewer: Not familiar with this tool. May have to correct that.
PATH problem: Doesn't feel likely; the Java code constructs a relative path to the executable that doesn't look like it's relying on any environment variables.
My thanks for the suggestions people have provided; at the very least, you've gotten my brain moving in directions that feel promising.
Solution Edit: And the winner is ... That's Not A Bug, That's A Feature! A feature gone horribly, horribly wrong. A feature that will now be neutered so as to stop bothering us.
A batch of invalid assumptions kept me from seeing it sooner, not the least of which was "I don't need to tool the code with more debug statements -- the statements already in there are telling me all I need to know!" DaDaDom, if you'd like to turn your comment into an answer, there's a shiny checkmark in it for you.
Thanks to everybody who chimed in with a suggestion. Now if you'll excuse me, my head is late for a meeting with my desk.

Here goes an answer:
Can you create a version of the software with verbose logging or could you even debug the code? At least then you can tell if it's in the java or the VB part.

Hmmmm. I've been told that executing programs from Java is either easy or hard. The easy part is starting them up. The hard part is dealing with the I/O streams (see my earlier question on using Runtime.exec()). Maybe the VB program is doing or expecting something weird on these particular machines that the Java code isn't working with properly.
edit: I also found a link to Jakarta Commons Exec:
Rationale
Executing external processes from Java is a well-known problem area. It is inheriently platform dependent and requires the developer to know and test for platform specific behaviors, for example using cmd.exe on Windows or limited buffer sizes causing deadlocks. The JRE support for this is very limited, albeit better with the new Java SE 1.5 ProcessBuilder class.
Reliably executing external processes can also require knowledge of the environment variables before or after the command is executed. In J2SE 1.1-1.4 there is not support for this, since the method, System.getenv(), for retriving environment variables is deprecated.
There are currently several different libraries that for their own purposes have implemented frameworks around Runtime.exec() to handle the various issues outlined above. The proposed project should aim at coordinating and learning from these initatives to create and maintain a simple, reusable and well-tested package. Since some of the more problematic platforms are not readily available, it is my hope that the broad Apache community can be a great help.

Have you considered the possibility that the authenticated user may not have permission to edit volume settings on the workstation? Does the program run correctly if you run as an 'Administrator'?

Java on OpenVMS?

We run batch files on our OpenVMS Alpha and Integrity servers. Up until now they have been written in COBOL. As you can imagine there are many reasons why will not be able to maintain that process.
At the same time we have a team of developers that use Eclipse and know Java very well. Is there away to use Eclipse with OpenVMS?

Maybe it's because I don't keep up with COBOL, but I am not sure why you're convinced you have to abandon it. I realize it's not the "in" thing, but if you already have a large code base I'd think at least twice before switching to another language. If it's a lack of developers, I don't think you're going to run out that soon.
That said, googling Eclipse & OpenVMS gave this link:
http://www.sdtimes.com/SearchResult/32973
So it looks like you can still get Eclipse for OpenVMS from eCube. If I'm reading that article correctly, HP seems to want you to go the NetBeans directions. Personally, I'm still using Emacs (and not currently doing any Java), so won't make a recommendation; I just wanted to point out that there are other ways to develop Java than Eclipse.
I didn't find Java for VMS on Sun's site (someone feel free to correct me if you find it), but it looks like you can get the JDK from HP/Compaq at:
http://www.compaq.com/java/download/ovms/1.5.0/index.html
Edit: I meant, but forgot to say: Assuming you're using a JVM on the VMS side, you should be able to development with Eclipse on another platform, and copy the byte code to the Alphas.

Speaking from experience, if you do decide to rewrite your batch processes in Java I'd suggest you use a third party batching framework like Spring Batch instead of 'growing your own'.
Using a framework also constrains you to work within a standard and should provide non-functional requirements like re-runability, transactions and error handling.
We've (re)built a number of batch processes from various technologies to Java using a home-grown framework and I find we end up spending time on fixing/optimizing the framework rather than just focusing on the business logic.

Don't leave Cobol yet - call a-cobol-programmer-thinking-about-switching-to-the-modern-world and make a trade: you teach him Java, He maintains your legacy.

Shell scripts and java usually aren't a great mix. You may want to consider installing a JVM on your VMS servers, and using one of the JVM-hosted languages that handle that case better- jython, jruby, or groovy might be candidates to consider.

Eclipse relies on native Java extensions that do not appear to have been ported to OpenVMS. Don't give up though. Java runs on OpenVMS (at least 1.5 according to a Google search).
NetBeans has a Java only edition that should work on OpenVMS. On the NetBeans Download Page select the OS Independent Zip option for the platform.

Are you running the batch files on your OpenVMS system? If so, HP makes Java available for OpenVMS, not SUN; you will have to look at their site. You can develop your java code on a windows/linux machine and test it on your VMS system; you must be aware of the native extensions that you cannot use on the VMS implementation of Java.

Speaking with some experience in this area, I suggest developing with Eclipse on your Windows/Linux/Mac desktop, and pushing the code out to OpenVMS for testing/deployment. Eclipse won't run on OpenVMS because of some platform-specific components of its GUI.
Some caveats:
Make sure that you are using the same version JVM on your desktop as on OpenVMS.
The case insensitivity in OpenVMS can be a problem when using inherently case-sensitive Java .class files. Package everything in a .jar and deploy it that way.
The attributes on .jar files have to be set correctly or the OpenVMS JVM can't open them. The following command should do the trick:
SET FILE *.jar /ATTR=(RFM:STMLF,RAT:CR)
HP provides both a "fast" JVM and a "classic" JVM. Use the fast VM unless your memory needs are highly variable.

I realize this question is rather old, but I was shocked nobody mentioned this book covering Java on OpenVMS.
https://www.theminimumyouneedtoknow.com/java_book.html
What really matters when using an x86 editor on OpenVMS source is your file transfer software. OpenVMS (and many other midrange ASCII based platforms) use even though most PC developers say LineFeed Carriage Return, the data files typically store it in the other order.
You can read much more about that here:
https://www.logikalsolutions.com/wordpress/information-technology/most-text-editors-get-tabs-wrong/
Your file transfer software will need to perform text mode file transfer changing the line ending characters OR your editor needs to both use and respect the better systems line ending characters. I thought there was something in Eclipse (via plug-in) to handle this. Notepadqq claims to have something.
Note this: They use Eclipse for development, not just editing.
That means they are running and debugging in their own PC based Eclipse universe and that ain't how it's going to work on OpenVMS. They are going to need a terminal into the VMS system and it needs to be a REAL VT-100 terminal emulator, not the worthless free stuff. You can read a little bit more about that here:
https://www.logikalsolutions.com/wordpress/information-technology/diamond-edt-keypad-support/
and here
https://www.logikalsolutions.com/wordpress/information-technology/xterm-and-vt-emulation/
Depending on how old your system is, you might have Pathworks installed and running. Then a system manager can create a directory for each user that they can map as a network drive to the PC. This lets the PC user use the directory like any other network disk and it generally could be configured to handle the line ending issues with text files.
There is no way they can develop on OpenVMS using Eclipse. They can edit files then test on OpenVMS, but they cannot develop within the IDE which I suspect is what they really want to do.
The only GUI that ever existed for OpenVMS was DECWindows. You had to run it on either a VAXStation or a DS model Alpha workstation. I never heard of Eclipse being ported to it. In the latest port of OpenVMS to x86 there is no GUI. It is a server only OS.
Yeah, I spent two decades on the platform and even wrote this book for it.

Yes, there is a version of Eclipse that supports OpenVMS called NXTware Remote. It has support for Java and COBOL languages as well as Fortran, Basic and Pascal.

You can edit OpenVMS files using pretty much any editor, including Eclipse - just use Samba to make OpenVMS directories and files visible to desktops on the network. If you install Java for OpenVMS, then you've got folks using Eclipse, and compiling and running on OpenVMS.
As for ditching Cobol - why? There's still a ton of companies running it, and it will certainly last for decades more.